The present invention relates to a nanostructured composite anode and a manufacturing method thereof, especially to an anode composite film with nano gas channels and an atmosphere plasma spray manufacturing method thereof. The nanostructured composite anode with nano gas channel applied to solid oxide fuel cells effectively improves the electrochemical activity as well as conductivity of the anode and reduces the anode resistance. Moreover, the power loss caused by anode resistance is cut back and nickel particle aggregation effect on increasing anode resistance to an unfavorable condition under high-temperature operation environment is slowed down. Therefore, the lifetime of the anode is increased.
Solid oxide fuel cell is an electrochemical device that converts the chemical energy in gaseous fuels such as hydrogen and natural gas into electrical energy. Generally, typical SOFC systems employ yttria stabilized zirconia (YSZ) as an electrolyte, nickel-yttria stabilized zirconia cermet (YSZ//Ni) as an anode, and perovskite conducting oxides such as lanthanum manganites (LaMnO3) as a cathode. Please refer to the following articles: Appleby, “Fuel cell technology: Status and future prospects,” Energy, 21, 521, 1996; Singhal, “Science and technology of solid-oxide fuel cells,” MRS Bulletin, 25, 16, 2000; Williams, “Status of solid oxide fuel cell development and commercialization in the U.S.,” Proceedings of 6th International Symposium on Solid Oxide Fuel Cells (SOFC VI), Honolulu, Hi., 3, 1999; Hujismans et al., “Intermediate temperature sofc—a promise for the 21th century,” J. Power Sources, 71, 107, 1998. The fuel cell needs to run at high temperatures—from 900 to 1000 Celsius degrees in order to achieve sufficiently oxygen conductivity and power output so that each material must have enough stability to endure fabrication and operation at high temperatures. Thus the manufacturing cost of such cells is quite high and it's difficult to do mass production of solid oxide fuel cells even such cells have high efficiency and low pollution.
Some electrolyte material has high oxygen conductivity at about 600° C. such as gadolinium-doped ceria (GDC). Compared with conventional technology, it's easier to use such electrolyte to manufacture fuel cell stack with lower cost. Along with decreasing of operation temperature, the reliability and lifetime of solid oxide fuel cells are dramatically improved and this further promotes applications of solid oxide fuel cells to vehicles or home use. However, when the operation temperature of solid oxide fuel cells falls into about 600° C., the electrochemical properties of electrodes decreases. This causes increasing of polarization resistance of anode and cathode. Thus besides new materials for the anode and the cathode such as LSCF(La0.6Sr0.4Co0.2Fe0.8O3) and Ni/GDC, improvement on microstructure of anode and cathode electrodes is required for a strong increase in the three-phase boundary so as to improve electrochemical activity and reduce power loss of the anode as well as the cathode.
There are a plurality of methods for manufacturing anodes of solid oxide fuel cells such as (1)chemical vapor deposition, (2)electrochemical vapor deposition, (3)sol-gel coating, (4)strip casting, (5) screen printing, (6) physical vaporous deosition and (7) plasma spray. The plasma spray includes atmosphere plasma spray (APS) and vacuum plasma spray (VPS). Among these methods, the manufacturing process of the atmosphere plasma spay is the fastest and has been received a lot of attentions.
Virkar has revealed a nanostructured YSZ/Ni cermet as anode for lower temperature and high power solid oxide fuel cells (Virkar, “Low-temperature anode-supported high power density solid oxide fuel cells with nanostructured electrodes,” Fuel Cell Annual Report, 111, 2003). The YSZ/Ni cermet consists of thin micro-pore layer and thick macro-pore layer while diameters of micro-pores are as smaller as possible such as in nano-scale for effectively increasing numbers of the TPB (triple-phase-boundary). However, it is not described in detailed about the nanostructure of this thin micro-pore layer. In 2003, Chinese chemist Jin-Xia Wang has reported a cermet anode formed by nano-scale NiO and micro-scale YSZ mixture through hydrogen reduction. The solid oxide fuel cell with such anode has a higher output power (Wang, “Influence of size of NiO on the electrochemical properties for SOFC anode,” Chemical Journal of Chinese Universities). In 2004, Liu also revealed nanostructured and functionally graded cathodes produced by Combustion Chemical Vapor Deposition (Liu, “Nanostructured and functionally graded cathodes for intermediate temperature solid oxide fuel cells,” J. Power Sources, 138, 194, 2004). In such a structure, number of chemical reaction sites or TPB is increased so that the polarization resistance is significantly decreased. The energy loss is minimized. But on references, there is no one reported nanostructured anode having nano gas channels manufactured by atmosphere plasma spray method.
Under high operation temperature, nickel particle aggregation happens in the YSZ/Ni or GDC/Ni cermet anode and the resistance increases along with the enlargement of nickel particles. When the anode resistance is too high, the fuel cell works inefficiently and is given up.
Thus the present invention provides a nanostructured composite anode with nano gas channels and an atmosphere plasma spray manufacturing method thereof. The nanostructured composite anode with nano gas channels is made from nanoparticles and is able to slow down aggregation of nickel metal iron under high temperature environment. Thus electrochemical activity and lifetime of the anode are improved. Moreover, the nanostructured composite anode having nano gas pores and nano gas channels increases the TPB length and numbers of reaction sites so as to improve electrochemical activity of the SOFC anode. The nanostructured composite anode with nano gas pores and nano gas channels also increases conductivity of the anode and reduce energy loss from anode resistance.